Look What I Can Do Now!

You won't believe the things I can do now!

—A great many characters written by Simon Furman, Transformers

Occasionally, a character will either see fit to train, or, in some cases, be forced to train. This will take them away from their core group for a while, but they'll Take A Level In Badass and come back stronger than ever.

Usually, though, during their absence, the core group will have to undertake a perilous journey or fight a group of enemies without Character X. One bad guy will give them trouble, and just when all hope seems lost, Character X will appear and brutally manhandle the foe.

Character X likely went through Training from Hell to acquire this new strength, or had someone tell them Time to Unlock More True Potential. Compare Took a Level in Badass, which doesn't require leaving the core group, and Big Damn Heroes which doesn't require a training arc.

Examples of Look What I Can Do Now! include:

Anime and Manga

Yuusuke from Yu Yu Hakusho goes away for six months between arcs to train with his new mentor Genkai, and returns with lots of nifty new techniques that he immediately has to use, since the second main story arc begins the same day he gets back. This is despite the fact that said training took six months, during which nothing at all happened, not even leadup—his training timeskips us directly to the day of his return and is only ever mentioned again in flashbacks.
Bleach does this with Kurosaki Ichigo; first when he unveils his brand new bankai in battle against Kuchiki Byakuya, and then when he uses his hollow mask against Grimmjow for the first time.
- Bleach is filled to the brim with those.

Ichigo : I can see you now, Kuchiki Byakuya !

- This also happens with Ishida Uryu after he loses his powers, then gets them back some eighty episodes later, finally showing them off almost twenty episodes after that. Fortunately, it's a pretty Badass return.
- Ichigo after training in Dangai then he proceeds to curb-stomp One-Winged Angel Aizen.
- And then again after completing his Fullbring. And shortly yet again, when he loses the Fullbring but regains his Shinigami powers.
Done in the manga version of Fullmetal Alchemist when Ran Fan reappeared after losing her arm by making mincemeat of Gluttony with her new Automail, saving Ed and Lin /Greed.
- And then we have Scar with his newly-revealed ability to deconstruct AND RECONSTRUCT. WHAM!
In Mahou Sensei Negima, after learning Evangeline's Black Magic, Negi gets a chance to show off just how powerful he's become, ripping through a group of supposedly ruthless and powerful bounty hunters after Kaede and Setsuna.
- He does it again later after perfecting his Thousand Bolts spell, this time beating the crap out of Jack Rakan.
  - Taken to ridiculous levels in that same fight. In every chapter of the fight so far, barring the flashback-heavy ones, Negi pulls out one or two never-before-seen techniques. Somewhat subverted in that he still can't beat Rakan. They end up fighting to a draw.
In the final segments of Magical Girl Lyrical Nanoha Sound Stage X, which is set three years after the events of the third season, Teanna reveals Nanoha's parting gift to her which she had been working on since we've last seen her and helps Subaru escape from the burning Marine Garden by using every cartridge she has and uttering two words: Starlight. Breaker.
In the Shaman King manga, it is said that a shaman can only increase his spiritual power after a close encounter with the spirit world (i.e. death and resurrection and/or near-death experience). The closer the shaman gets to death, the larger the factor of the ability increase.
One cannot forget Naruto, who practically uses this as his standard way of fighting. Heck, he does it in the first episode/volume when he first busts out what will become his signature move, not to mention twice first when he shows up against a nigh-immortal opponent to backstab him with a newly-developed technique that seems to function like a blender crossed with an artillery shell, and second when he is summoned back to the village and starts wiping the floor with the seemingly-invincible Pain using his newly-learned "Sage Mode". Then later after taking control of Kyuubi's power he can among other things make Mini-Rasenshuriken and Beam Spam them, turning him into a One Man Badass Army.
Soul Eater: Black Star's return in the Baba Yaga arc. He left after a series of defeats led him to find a different way to train and figure out the Nakatsukasa Purpose. He comes back knocking aside every Arachnaphobia mook unfortunate enough to be in his path (his presence enough that Kid can sense his soul from the middle of the castle), and arrives in time to fight Mifune with an impressive new set of techniques and lend a hand in taking down the pseudo-Kishin Arachne by, typically, sheer force of will.
Kenichi: The Mightiest Disciple combines this with My Kung Fu Is Stronger Than Yours, but with an (anti-)villain instead of the hero. Tsuji Shinnosuke (a.k.a. "the crazy-haired one") of the Ragnarok gang, after being defeated by Kenichi, withdraws into wilderness and trains hard to become stronger. When he eventually returns, he is appalled when finding out that his former gang has been disbanded after their key members had all been defeated by Kenichi.
- This is played for laughs. Despite the training Shinnosuke went through, Kenichi has absolutely no interest in fighting him. Then, when they finally do fight, Kenichi demonstrates that he is significantly stronger than him. However, when Kenichi becomes distracted, Shinnosuke manages a lucky punch and knocks him out. When Kenichi awakens, he immediately demands a rematch, but Shinnosuke refuses and leaves, saying that he's never going to fight Kenichi again.
Dragon Ball Z did this four times, actually:

When Goku came Back from the Dead and made a fool of Nappa (by showing that his power level was Over Nine Thousand),
During the Ginyu Force arc, when Goku returned to the fray and mopped the floor with most of Ginyu's subordinates.
When he comes back from Training IN SPACE! to demonstrate his "Instant Transmission," and
When Vegeta showed up after some training and destroyed Android 19.
And a psuedo-fifth if you count his return from Otherworld in the Buu Saga. Even though he never defeated anybody with it, he surprised everyone when he revealed that he discovered and mastered Super Saiyan 3. And actually didn't use it during his fight with Vegeta so that he wouldn't invoke this and embarrass him. (When Vegeta found out that Goku was holding back during their fight, he was pissed.)

- Note that all four examples involve Saiyans. The race actually has a biological ability to come back from severe beatdowns and/or death much, much stronger than before, leading to heavy use of this trope.
Both Suzaku and Kallen get this in Code Geass when they get the final versions of their personal mecha. Kallen shows off the Guren SEITEN's energy wings and wired radiant wave arm in its debut battle, as well as effortlessly destroying a Knight of the Round and handing Suzaku his ass on a platter. The debut of the Lancelot Albion has Suzaku facing off against four Knights of the Round, killing the two women without breaking a sweat and performing a Diagonal Cut on his former boss Bismarck.
- To some extent, Lelouch gets this with the debut of the Shinkirou, showing off its battleship-level Beehive Barrier and its scattering laser weapon at the climax of the Chinese Federation story arc.
One Piece doesn't do this too often—especially considering its Long Runner status (Usually because the characters learn the new moves as they go), but it does have a few points to note:
- A few instances in the Water 7 arc, most notably Nami's Perfect Clima-Tact and Luffys Gears.
- Coby, returning after taking a few levels in badass.
- The entire New Fishman Pirates arc is this. The crew essentially one-shotted a group of BigBads that seemed to be a perfectly logical next step in the series' Sorting Algorithm of Evil by showing off their new moves.
Fairy Tail sees the strongest wizards in the guild Put on a Bus over a seven-year-long Time Skip, and return to find that their minor-character friends have grown so strong, they can actually give the main character Natsu, one of the strongest members of the guild, a run for his money. Later on, Ultear gives a Power-Up to the main cast so they can have a fighting chance for an upcoming tournament, and they're suddenly able to do twice as much as they've been able—most prominent is Lucy, who is known to succumb to fatigue after summoning multiple spirits one at a time and one after the other, but can now summon two at once without breaking a sweat..

Comic Books

Transformers who get upgraded make a habit of doing this, especially in Beast Wars.
- In an issue of the Marvel comics, this happens to one character right before a fight breaks out, immobilizing him in a sort of chrysalis, and just as the good guys seem to be on the ropes, the new character breaks free of his cocoon and goes to town.
All-Star Superman has a couple of these. When Superman is powered up by intense sun exposure in the first issue, he immediately extends a bioelectric aura around Quintum's sunship. Later he performs a number of super-feats employing newly acquired super-intelligence (although this is sort of a power that Superman has had on and off over the years.)

Film

Played mostly straight in Kung Fu Panda: the Furious Five take on Tai Lung and are soundly trounced all while Po is off training to be a true master. After it appears the Dragon Scroll is useless, Shifu takes on his former pupil all alone. It doesn't work. Finally, Po shows up and sits on Tai Lung's face.

Professional Wrestling

This is pretty much the standard way to break up a Professional Wrestling tag team; one partner will turn on and injure the other, putting him out of action for several months. He'll then run rampant through the midcard until his former partner returns from injury out of nowhere and beats the snot out of him.

Video Games

This also appeared in Final Fantasy IV. Golbez appears and wipes the floor with Cecil's group, until Rydia returns and effectively destroys Golbez's summon.
It happened in EarthBound, when Poo returned from training and demonstrated his new power on a boss creature, obliterating it with PK Starstorm.
This also happens in Mother 3 during this battle.
In Project Justice, the sequel to Rival Schools, if you should lose as Batsu early in the Taiyo High storyline, he'll go away from his core team for a while, and then come back battle-scarred, but stronger than ever.
In Super Robot Wars games where there are route splits with different major plot events that give a particular character/mecha a new ability or a character gets an entirely new mech, this trope is often invoked if you field the unit you just got back.